Seam concealment for three-dimensional models

ABSTRACT

A three-dimensional model built with an extrusion-based digital manufacturing system, and having a perimeter based on a contour tool path that defines an interior region of a layer of the three-dimensional model, where at least one of a start point and a stop point of the contour tool path is located within the interior region of the layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.13/707,884, filed Dec. 7, 2012; which is a Divisional of U.S. patentapplication Ser. No. 12/565,397, filed Sep. 23, 2009, and granted asU.S. Pat. No. 8,349,239.

BACKGROUND

The present disclosure relates to direct digital manufacturing systemsfor building three-dimensional (3D) models. In particular, the presentinvention relates to techniques for building 3D models withextrusion-based digital manufacturing systems.

An extrusion-based digital manufacturing system (e.g., fused depositionmodeling systems developed by Stratasys, Inc., Eden Prairie, Minn.) isused to build a 3D model from a digital representation of the 3D modelin a layer-by-layer manner by extruding a flowable consumable modelingmaterial. The modeling material is extruded through an extrusion tipcarried by an extrusion head, and is deposited as a sequence of roads ona substrate in an x-y plane. The extruded modeling material fuses topreviously deposited modeling material, and solidifies upon a drop intemperature. The position of the extrusion head relative to thesubstrate is then incremented along a z-axis (perpendicular to the x-yplane), and the process is then repeated to form a 3D model resemblingthe digital representation.

Movement of the extrusion head with respect to the substrate isperformed under computer control, in accordance with build data thatrepresents the 3D model. The build data is obtained by initially slicingthe digital representation of the 3D model into multiple horizontallysliced layers. Then, for each sliced layer, the host computer generatesone or more tool paths for depositing roads of modeling material to formthe 3D model.

In fabricating 3D models by depositing layers of a modeling material,supporting layers or structures are typically built underneathoverhanging portions or in cavities of objects under construction, whichare not supported by the modeling material itself. A support structuremay be built utilizing the same deposition techniques by which themodeling material is deposited. The host computer generates additionalgeometry acting as a support structure for the overhanging or free-spacesegments of the 3D model being formed. Consumable support material isthen deposited from a second nozzle pursuant to the generated geometryduring the build process. The support material adheres to the modelingmaterial during fabrication, and is removable from the completed 3Dmodel when the build process is complete.

SUMMARY

A first aspect of the present disclosure is directed to a method forbuilding a 3D model with an extrusion-based digital manufacturingsystem. The method includes generating a contour tool path that definesan interior region of a layer of the 3D model, where the contour toolpath comprises a start point and a stop point, and where at least one ofthe start point and the stop point is located within the interior regionof the layer.

Another aspect of the present disclosure is directed to a method forbuilding a 3D model with an extrusion-based digital manufacturingsystem, where the method includes receiving data comprising tool pathsfor building a plurality of layers of the 3D model. The method alsoincludes extruding a material in a pattern based on the tool paths toform a perimeter of the extruded material for one of the layers of the3D model, where the perimeter has a start point and a stop point, anddefines an interior region of the layer, and where at least one of thestart point and the stop point is located within the interior region ofthe layer.

Another aspect of the present disclosure is directed to a 3D model builtwith an extrusion-based digital manufacturing system. The 3D modelincludes a plurality of layers of an extruded material, where at leastone of the layers includes a perimeter of the extruded material, andwhere the perimeter has a start point and a stop point. The layer alsoincludes an interior region defined by the perimeter, where at least oneof the start point and the stop point is located within the interiorregion of the layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of an extrusion-based digital manufacturingsystem for building 3D models and support structures.

FIG. 2 is a top view of a layer of a 3D model being built with theextrusion-based digital manufacturing system.

FIG. 3 is an expanded view of section 3 taken in FIG. 2, illustrating aseam of the layer with an open-square arrangement.

FIG. 4 is a flow diagram of a method for generating data and building a3D model having concealed seams.

FIG. 5 is an alternative expanded view of section 3 taken in FIG. 2,illustrating a seam of a first alternative layer with a closed-squarearrangement.

FIG. 6 is an alternative expanded view of section 3 taken in FIG. 2,illustrating a seam of a second alternative layer with an overlappedclosed-square arrangement.

FIG. 7 is an alternative expanded view of section 3 taken in FIG. 2,illustrating a seam of a third alternative layer with an open-trianglearrangement.

FIG. 8 is an alternative expanded view of section 3 taken in FIG. 2,illustrating a seam of a fourth alternative layer with a closed-trianglearrangement.

FIG. 9 is an alternative expanded view of section 3 taken in FIG. 2,illustrating a seam of a fifth alternative layer with a converging-pointarrangement.

FIG. 10 is an alternative expanded view of section 3 taken in FIG. 2,illustrating a seam of a sixth alternative layer with anoverlapped-cross arrangement.

FIG. 11 is an alternative expanded view of section 3 taken in FIG. 2,illustrating a seam of a seventh alternative layer with a combinedperimeter and raster pattern arrangement, where a start point is locatedadjacent to the seam and a stop point is located within an interiorregion.

FIG. 12 is an alternative expanded view of section 3 taken in FIG. 2,illustrating a seam of an eighth alternative layer with a combinedperimeter and raster pattern arrangement, where start and stop pointsare each located within an interior region.

FIG. 13 is an alternative expanded view of section 3 taken in FIG. 2,illustrating a seam of a ninth alternative layer with an crimped-squarearrangement.

FIG. 14 is a top view of a tenth alternative layer of the 3D model beingbuilt with the extrusion-based digital manufacturing system.

FIG. 15 is an expanded view of section 15 taken in FIG. 14, illustratinga seam of the tenth alternative layer with a step-over arrangement.

FIG. 16 is an alternative expanded view of section 15 taken in FIG. 14,illustrating a seam of an eleventh alternative layer with a shortenedstep-over arrangement.

DETAILED DESCRIPTION

The present disclosure is directed to a method for building 3D modelswith deposition patterns that contain concealed seams. As discussedbelow, the method involves adjusting the start point and/or the stoppoint of a contour tool path of a 3D model layer to one or morelocations that are within an interior region of the layer. Thiseffectively conceals the seam that is formed at the intersection of thestarting and stop points, which can increase the aesthetic andfunctional qualities of the resulting 3D model.

The following discussion of 3D models with concealed seams is made withreference to 3D models built with modeling materials since consumers aregenerally more concerned about the aesthetic and physical qualities ofthe intended 3D models, and are less concerned about such qualities ofthe “support materials” used to form support structures, which aretypically removed and discarded. However, the techniques for formingconcealed seams may also be used to form support structures havingconcealed seams. Thus, the term “three-dimensional model” may apply to a3D model built with a modeling material and to a support structure builtwith a support material.

FIG. 1 is a front view of system 10 in use with computer 12, wheresystem 10 is an extrusion-based digital manufacturing system that may beused to build 3D models and/or support structures with concealed seams.As shown, system 10 includes build chamber 14, platen 16, gantry 18,extrusion head 20, and supply sources 22 and 24. Suitableextrusion-based digital manufacturing systems for system 10 includefused deposition modeling systems developed by Stratasys, Inc., EdenPrairie, Minn.

Build chamber 14 is an enclosed, heatable environment that containsplaten 16, gantry 18, and extrusion head 20 for building a 3D model(referred to as 3D model 26) and a corresponding support structure(referred to as support structure 28). Platen 16 is a platform on which3D model 26 and support structure 28 are built, and moves along avertical z-axis based on signals provided from controller 30. Asdiscussed below, controller 30 directs the motion of platen 16 andextrusion head 20 based on data supplied by computer 12.

Gantry 18 is a guide rail system configured to move extrusion head 20 ina horizontal x-y plane within build chamber 14 based on signals providedfrom controller 30. The horizontal x-y plane is a plane defined by anx-axis and a y-axis (not shown in FIG. 1), where the x-axis, the y-axis,and the z-axis are orthogonal to each other. In an alternativeembodiment, platen 16 may be configured to move in the horizontal x-yplane within build chamber 14, and extrusion head 20 may be configuredto move along the z-axis. Other similar arrangements may also be usedsuch that one or both of platen 16 and extrusion head 20 are moveablerelative to each other.

Extrusion head 20 is supported by gantry 18 for building 3D model 26 andsupport structure 28 on platen 16 in a layer-by-layer manner, based onsignals provided from controller 30. Accordingly, controller 30 alsodirects extrusion head 20 to selectively deposit the modeling andsupport materials based on data supplied by computer 12. In theembodiment shown in FIG. 1, extrusion head 20 is a dual-tip extrusionhead configured to deposit modeling and support materials from supplysource 22 and supply source 24, respectively.

Examples of suitable extrusion heads for extrusion head 20 include thosedisclosed in LaBossiere, et al., U.S. Patent Application PublicationNos. 2007/0003656 and 2007/00228590; and Leavitt, U.S. PatentApplication Publication No. 2009/0035405. Alternatively, system 10 mayinclude one or more two-stage pump assemblies, such as those disclosedin Batchelder et al., U.S. Pat. No. 5,764,521; and Skubic et al., U.S.Patent Application Publication No. 2008/0213419. Furthermore, system 10may include a plurality of extrusion heads 18 for depositing modelingand/or support materials.

The modeling material may be provided to extrusion head 20 from supplysource 22 through pathway 32. Similarly, the support material may beprovided to extrusion head 20 from supply source 24 through pathway 34.System 10 may also include additional drive mechanisms (not shown)configured to assist in feeding the modeling and support materials fromsupply sources 22 and 24 to extrusion head 20.

The modeling and support materials may be provided to system 10 in avariety of different media. For example, the modeling and supportmaterials may be provided as continuous filaments fed respectively fromsupply sources 22 and 24, as disclosed in Swanson et al., U.S. Pat. No.6,923,634; Comb et al., U.S. Pat. No. 7,122,246; and Taatjes et al, U.S.Patent Application Publication Nos. 2010/0096489 and 2010/0096485.Examples of suitable average diameters for the filaments of the modelingand support materials range from about 1.27 millimeters (about 0.050inches) to about 2.54 millimeters (about 0.100 inches), withparticularly suitable average diameters ranging from about 1.65millimeters (about 0.065 inches) to about 1.91 millimeters (about 0.075inches). Alternatively, the modeling and support materials may beprovided as other forms of media (e.g., pellets and resins) from othertypes of storage and delivery components (e.g., supply hoppers andvessels).

Suitable modeling materials for building 3D model 26 include materialshaving amorphous properties, such as thermoplastic materials, amorphousmetallic materials, and combinations thereof. Examples of suitablethermoplastic materials for ribbon filament 34 includeacrylonitrile-butadiene-styrene (ABS) copolymers, polycarbonates,polysulfones, polyethersulfones, polyphenylsulfones, polyetherimides,amorphous polyamides, modified variations thereof (e.g., ABS-M30copolymers), polystyrene, and blends thereof. Examples of suitableamorphous metallic materials include those disclosed in U.S. patentapplication Ser. No. 12/417,740.

Suitable support materials for building support structure 28 includematerials having amorphous properties (e.g., thermoplastic materials)and that are desirably removable from the corresponding modelingmaterials after 3D model 24 and support structure 26 are built. Examplesof suitable support materials for ribbon filament 34 includewater-soluble support materials commercially available under the tradedesignations “WATERWORKS” and “SOLUBLE SUPPORTS” from Stratasys, Inc.,Eden Prairie, Minn.; break-away support materials commercially availableunder the trade designation “BASS” from Stratasys, Inc., Eden Prairie,Minn., and those disclosed in Crump et al., U.S. Pat. No. 5,503,785;Lombardi et al., U.S. Pat. Nos. 6,070,107 and 6,228,923; Priedeman etal., U.S. Pat. No. 6,790,403; and Hopkins et al., U.S. PatentApplication Publication No. 2010/0096072.

Prior to a build operation, computer 12 may receive a digitalrepresentation of 3D model 26. Computer 12 is one or more computer-basedsystems that communicates with system 10 (e.g., with controller 30), andmay be separate from system 10, or alternatively may be an internalcomponent of system 10. Upon receipt of the digital representation of 3Dmodel 26, computer 12 may reorient the digital representation andgenerate one or more supports for any overhanging regions that requirevertical support (e.g., with support structure 28).

Computer 12 may then slice the digital representation and generatedsupports into multiple layers. For each layer, computer 12 may thengenerate one or more tool paths for extrusion head 20 to follow forbuilding each layer of 3D model 26 and support structure 28. Thegeneration of the tool path(s) for a layer of 3D model 26 may initiallyinvolve generating one or more contour tool paths that define theperimeter(s) of 3D model 26 for the given layer. As discussed below,computer 12 also desirably adjusts the start point and/or the stop pointof each contour tool path of the layer to one or more locations that arewithin an interior region of the layer defined by the respective contourtool path. This effectively conceals the seam that is formed at theintersection of the start and stop points.

Based on each generated contour tool path, computer 12 may then generateone or more additional tool paths (e.g., raster paths) to fill in theinterior region(s) defined by the perimeter(s), as necessary. As furtherdiscussed below, the generation of the additional tool path(s) (e.g.,raster paths) desirably compensate for the adjustments in the locationsof the start points and/or the stop points of the contour tool path(s).

One or more tool paths for the layer of support structure 28 may also begenerated in the same manner. This process may then repeated be for eachsliced layer of the digital representation, and the generated data maybe stored on any suitable computer storage medium (e.g., on a storagedevice of computer 12). The generated data may also be transmitted fromcomputer 12 to controller 30 for building 3D model 26 and supportstructure 28.

During a build operation, controller 30 directs one or more drivemechanisms (not shown) to intermittently feed the modeling and supportmaterials to extrusion head 20 from supply sources 22 and 24. For eachlayer, controller 30 then directs gantry 18 to move extrusion head 20around in the horizontal x-y plane within build chamber 14 based on thegenerated tool paths. The received modeling and support materials arethen deposited onto platen 16 to build the layer of 3D model 26 andsupport structure 28 using the layer-based additive technique.

The formation of each layer of 3D model 26 and support structure 28 maybe performed in an intermittent manner in which the modeling materialmay initially be deposited to form the layer of 3D model 26. Extrusionhead 20 may then be toggled to deposit the support material to form thelayer of support structure 28. The reciprocating order of modeling andsupport materials may alternatively be used. The deposition process maythen be performed for each successive layer to build 3D model 26 andsupport structure 28. Support structure 28 is desirably deposited toprovide vertical support along the z-axis for overhanging regions of thelayers of 3D model 26. After the build operation is complete, theresulting 3D model 26/support structure 28 may be removed from buildchamber 14, and support structure 28 may be removed from 3D model 26.

FIGS. 2 and 3 illustrate layer 36, which is a layer of 3D model 26formed by depositing a modeling material with system 10. As shown inFIG. 2, layer 36 includes perimeter path 38, which is a road of amodeling material that is deposited by extrusion head 20 along contourtool path 40. As discussed above, contour tool path 40 may be generatedby computer 12 based on road width 42, which is a predicted width of adeposited road of the modeling material, and may depend on a variety offactors, such as modeling material properties, the type ofextrusion-based digital manufacturing system used, extrusion conditions,extrusion tip dimensions, and the like. Suitable widths for road width42 range from about 250 micrometers (about 10 mils) to about 1,020micrometers (about 40 mils), with particularly suitable widths rangingfrom about 380 micrometers (about 15 mils) to about 760 micrometers(about 30 mils).

In the current example, the modeling material is deposited along contourtool path 40 in a clockwise direction, as represented by arrows 44, toform perimeter path 38. Alternatively, the modeling material may bealong contour tool path 40 in a counter-clockwise direction. Perimeterpath 38 includes exterior surface 46 and interior surface 48, which areeach offset from contour tool path 40 by about one-half of road width42. Exterior surface 46 is the outward-facing surface of perimeter path38 and may be observable when 3D model 26 is completed. Interior surface48 is the inward-facing surface of perimeter path 38, which definesinterior region 50. Interior region 50 is the region of layer 36confined within perimeter path 38, and may be filled with additionalmodeling material deposited along additionally generated tool paths(e.g., raster paths, not shown).

As shown in FIG. 3, contour tool path 40 includes start point 52 andstop point 54, where start point 52 is a first location in the x-y planeat which extrusion head 20 is directed to begin depositing the modelingmaterial, and stop point 54 is a second location in the x-y plane atwhich extrusion head 20 is directed to stop depositing the modelingmaterial. Accordingly, during the build operation, controller 30 directsextrusion head 20 to begin depositing the modeling material at startpoint 52, and to move along contour tool path 40 in the direction ofarrow 56 until reaching point 58. Extrusion head 20 is then directed tofollow the ring-geometry of contour tool path 40, as illustrated byarrows 44, until reaching point 60. Extrusion head 20 is then directedto move along contour tool path 40 in the direction of arrow 62 untilreaching stop point 54, where extrusion head 20 stops depositing themodeling material.

This process provides a continuous road of the deposited modelingmaterial at all locations around perimeter path 38 except at theintersection between points 58 and 60, where the outgoing and incomingroads meet. This intersection forms a seam for layer 36 (referred to asseam 64). As shown, start point 52 and stop point 54 are each located atan offset location from seam 64 within interior region 50. This is incomparison to start and stop points generated under a conventional datageneration technique, in which the start and stop points would typicallybe collinear with the outer ring of contour tool path 40 (i.e., atpoints 58 and 60, respectively). Under the conventional technique, acontour tool path is typically generated to match the geometry of theexterior perimeter of a 3D model layer, with an offset that accounts forthe road width (e.g., road width 42). Thus, the start and stop pointswould necessarily be located at locations that are collinear with thecontour tool path, and the stop point would end up being located next tothe start point (e.g., at points 58 and 60).

Due to variations in the extrusion process when starting and stoppingthe depositions, the modeling material deposited at a stop pointcorresponding to point 60 may bump into the modeling material previouslydeposited at a start point corresponding to point 58. This bumping canform a significant bulge of the modeling materials at the seam, whichcan be visually observed with the naked eye, thereby detracting from theaesthetic qualities of the resulting 3D model. Alternatively, if notenough modeling material is deposited between points 58 and 60, a gapmay be formed at the seam, which can increase the porosity of the 3Dmodel. The increased porosity can allow gases and fluids to pass into orthrough the 3D model, which may be undesirable for many functionalpurposes (e.g., for containing liquids). Accordingly, under theconventional data generation technique, proper seam sealing may bedifficult to achieve, particularly due to the number of geometriccomplexities that may be required for a given 3D model.

Pursuant to the method of the present disclosure, however, seam 64 maybe properly sealed by adjusting the location of the start point frompoint 58 to point 52, and by adjusting the location of the stop pointfrom point 60 to point 54. This allows any variations in the extrusionprocess when starting and stopping the depositions to occur at alocation that is within interior region 50 rather than adjacent toexterior surface 46. Any variations (e.g., bulges) that occur withininterior region 50 are masked by the successive layers of 3D model 26,thereby concealing these effects within the filled body of 3D model 26when completed. This allows the dimensions of perimeter path 38 at seam64 to be truer to the dimensions of the digital representation of 3Dmodel 26 and increases the consistency of the seams of successive layersof 3D model 26.

While shown at particular x-y coordinates within interior region 50,start point 52 and/or stop point 54 may alternatively be adjusted to avariety of different coordinate locations within interior region 50.Additionally, the coordinate locations may vary depending on thedimensions of the particular layer of the 3D model being built. In theembodiment shown in FIG. 3, start point 52 and stop point 54 areadjusted respectively from points 58 and 60 by vectors that areorthogonal to contour tool path 40 at perimeter path 38, and which pointtoward interior region 50. Examples of suitable distances for adjustingstart point 52 from point 58 and/or for adjusting stop point 54 frompoint 60 (i.e., from a centerline of perimeter path 38) includesdistances that are greater than 50% of road width 42 (i.e., beyondinterior surface 48), with particularly suitable distances ranging fromgreater than about 50% of road width 42 to about 200% of road width 42,and with even more particularly suitable distances ranging from about75% of road width 42 to about 150% of road width 42.

The locations of start point 52 and stop point 54 also allow thedeposited modeling material to form a seal at seam 64 that extendsinward within interior region 50. This reduces the porosity of 3D model26 at seam 64, thereby reducing or eliminating the transmission of gasesand/or liquids through seam 64. As a result, in comparison to theconventional techniques, the process of adjusting the start and stoppoints to locations within interior region 50 effectively eliminates theformation of bulges of modeling material at seam 64, while also reducingthe porosity at seam 64.

FIG. 4 is a flow diagram of method 66 for generating data and building a3D model based on a digital representation of the 3D model, where theresulting 3D model includes concealed seams. The following discussion ofmethod 66 is made with reference to 3D model 26 (shown in FIG. 1) andlayer 36 of 3D model 24 (shown in FIGS. 2 and 3). However, method 66 isapplicable for building 3D models and corresponding support structureshaving a variety of different geometries. As shown in FIG. 4, method 66includes steps 68-84, and initially involves receiving a digitalrepresentation of 3D model 24 (step 68), slicing the digitalrepresentation and into multiple layers (step 70), and generating one ormore pre-sliced support structures with computer 12 (step 72). In analternative embodiment, steps 70 and 72 may be reversed such that one ormore support structures are generated and the digital representation andthe generated support structure(s) are then sliced.

Computer 12 then selects a first layer of the sliced layers andgenerates one or more contour tool paths based on the perimeter of thelayer (step 74). For example, computer 12 may generate a contour toolpath that defines the outer ring for perimeter path 38. In alternativeexamples, a given layer may include multiple contour tool paths forbuilding multiple and separate parts and/or may include an exterior andan interior contour tool path for a single part (e.g., having a hollowinterior cavity). At this point, the start and stop points for eachgenerated contour tool path are collinear with the perimeter of thelayer.

Computer 12 may then adjust the locations of the start point and/or thestop point to coordinate locations that are within the interior regionfor each generated contour tool path (step 76). For example, computer 12may adjust the start point from point 58 to point 52, and may adjust thestop point from point 60 to point 54. This places start point 52 andstop point 54 within interior region 50. In an alternative embodiment,steps 74 and 76 of method 66 may be performed in a single step. In thisembodiment, the adjustment locations of the start and stop points may begenerated along with the generation of the contour tool path(s) (e.g.,as predefined offset locations).

After the start and stop points are positioned in the interior region ofthe layer (e.g., within interior region 50 of layer 36), computer 12 maythen generate additional tool paths (e.g., raster paths) to bulk fillthe interior region (step 78). In this step, the generated additionaltool paths desirably account for the locations of start point 52 andstop point 54, and the segments of contour tool path 40 that extend intointerior region 50. When the layer is completed, computer 12 may thendetermine whether the current layer is the last of the sliced layers(step 80). In the current example, layer 36 is not the last layer. Assuch, computer 12 may select the next layer (step 82) and repeat steps74-82 until the last layer is completed.

When the last layer is completed, computer 12 may transmit the resultingdata to system 10 for building 3D model 26 and support structure 28(step 84). During the build operation, extrusion head 20 follows thepatterns of the tool paths for each layer, including the contour toolpaths with the adjusted start and stop points. As such, each layer of 3Dmodel 26 and/or of support structure 28 may include a concealed seamhaving start and stop points located within the interior region of thegiven layer. Furthermore, the seams of adjacent layers may be offsetfrom each other, thereby further obscuring the locations of the seams.

FIGS. 5-13 are alternative sectional views of section 3 shown in FIG. 2,illustrating layers 136-936, which are alternatives to layer 36 (shownin FIGS. 2 and 3) having different start and stop points, and where thereferences labels are increased by 100-900, respectively. As shown inFIG. 5, layer 136 includes contour tool path 140 having start point 152and stop point 154 in a closed-square arrangement. In this embodiment,start point 152 is positioned at the same coordinate location withininterior region 150 as start point 52 (shown in FIG. 3). The location ofstop point 154, however, causes contour tool path 140 to turn at cornerpoint 186. As such, contour tool path 140 extends inward from point 160in the direction of arrow 162, and turns in the direction of arrow 188at corner point 186 toward stop point 154. This arrangement furtherreduces the porosity of layer 136 by creating a bend of the depositedroads of build material within interior region 150.

As shown in FIG. 6, layer 236 includes contour tool path 240 havingstart point 252 and stop point 254 in an overlapped closed-squarearrangement. In this embodiment, start point 252 and stop point 254 arepositioned at the same coordinate location within interior region 250(i.e., stop point 254 overlaps start point 252). This arrangement alsoincludes corner point 286, which bends contour tool path 240 in the samemanner as discussed above for corner point 186 (shown in FIG. 5), whichis beneficial for reducing porosity while also concealing seam 264.

The embodiment shown in FIG. 6 may be performed by gradually increasingthe volumetric flow rate of the modeling material as extrusion head 20travels between start point 252 and point 258, and also by graduallyreducing the reducing the volumetric flow rate of the modeling materialas extrusion head 20 travels between point 260 and stop point 254. Forexample, when extrusion head 20 travels along contour tool path 240between start point 252 and point 258 in the direction of arrow 256,controller 30 may direct extrusion head 20 to gradually increase thevolumetric flow rate from zero up to 100% of the standard operationalrate. Extrusion head 20 may then deposit the modeling material at 100%of the standard operational rate while forming perimeter path 238 alongarrows 244. Then, when extrusion head 20 travels along contour tool path240 between point 260 and stop point 254 in the directions of arrows 262and 288, controller 30 may direct extrusion head 20 to gradually reducethe volumetric flow rate from 100% of the standard operational rate downto zero. This process reduces the amount of modeling material that isaccumulated along the vertical z-axis at the intersection of start point252 and stop point 254.

As shown in FIG. 7, layer 336 includes contour tool path 340 havingstart point 352 and stop point 354 in an open-triangle arrangement. Inthis embodiment, start point 352 and stop point 354 extend at anglesrelative to the orthogonal directions of start point 52 and stop point54 (shown in FIG. 3). In this embodiment, the corner points that directcontour tool path 340 into and out of interior region 350 (i.e., points358 and 360) are desirably offset from each other by a distance that isabout 90% of road width 342 to about 100% of road width 342. This allowsseam 364 to be properly sealed at exterior surface 346 of perimeter path338.

As shown, start point 352 is positioned at a coordinate location withininterior region 350 that is offset at angle α from the orthogonal axisto contour tool path 340 at perimeter path 338 (i.e., taken at point358). Similarly, stop point 354 is positioned at a coordinate locationwithin interior region 350 that is offset at angle β from the orthogonalaxis to contour tool path 340 at perimeter path 338 (i.e., taken atpoint 360). Angles α and β may be the same values from their respectiveorthogonal axis, or may be different values, which may be affected bythe geometry of layer 336. Examples of suitable angles for each of angleα and angle β range from zero degrees (i.e., parallel to the orthogonalaxis, as shown in FIG. 3) to about 60 degrees, with particularlysuitable angles ranging from about 30 degrees to about 45 degrees. Theangled locations of start point 352 and stop point 354 reduce the extentthat start point 352 and stop point 354 extend into interior region 350.This is arrangement suitable for use with 3D models having thin-walledregions.

As shown in FIG. 8, layer 436 includes contour tool path 440 havingstart point 452 and stop point 454 in a closed-triangle arrangement. Inthis embodiment, start point 452 extends at an angle relative to theorthogonal direction of start point 52 (shown in FIG. 3) in a similarmanner to that discussed above for start point 352 (shown in FIG. 7).Furthermore, this arrangement includes corner point 486, which bendscontour tool path 440 in a similar manner to that discussed above forcorner point 186 (shown in FIG. 5). This combination further reducesporosity, and also further reduces the extent that start point 452 andstop point 454 extend into interior region 450. As such, this embodimentis also suitable for use with 3D models having thin-walled regions.

As shown in FIG. 9, layer 536 includes contour tool path 540 havingstart point 552 and stop point 554 in a converging-point arrangement. Inthis embodiment, start point 352 and stop point 354 are positionedcloser to each other compared to points 558 and 560. The corner pointsthat direct contour tool path 540 into interior region 550 (i.e., points558 and 560) are also desirably offset from each other by a distanceabout equal to the road width of perimeter path 538. As such, startpoint 552 and stop point 554 are offset from each other by a distancethat is less than the road width.

This embodiment may be performed by gradually increasing the volumetricflow rate of the modeling material as extrusion head 20 travels alongcontour tool path 540 in the direction of arrow 556 between start point552 and point 558. Similarly, as extrusion head 20 travels along contourtool path 540 in the direction of arrow 562 between point 560 and stoppoint 554, the volumetric flow rate may gradually decrease. This allowsproper amounts of modeling material to be deposited at seam 564 and alsoreduces the amount of modeling material that is accumulated along thevertical z-axis at the intersection between start point 552 and stoppoint 554.

As shown in FIG. 10, layer 636 includes contour tool path 640 havingstart point 652 and stop point 654 in an overlapped-cross arrangement.In this embodiment, the relative locations of start point 652 and stoppoint 654 cause contour tool path 640 to overlap at seam 664. Thisembodiment may also be performed by gradually adjusting the volumetricflow rate of the modeling material as extrusion head 20 travels alongcontour tool path 640. For example, the volumetric flow rate may bedecreased from 100% of the standard operational rate at point 660 downto zero at stop point 654. However, in this embodiment, it is desirablefor the volumetric flow rate of the modeling material to besubstantially decreased at or shortly after point 660 to reduce theamount of modeling material that is accumulated along the verticalz-axis a seam 664.

Accordingly, during a build operation, extrusion head 20 may initiallyfollow contour tool path 640 from start point 652 to point 658 in thedirection of arrow 656. The volumetric flow rate of the modelingmaterial may also be gradually increased at this stage. Extrusion head20 may then deposit the modeling material at 100% of the standardoperational rate while forming perimeter path 638 along arrows 644.Then, extrusion head 20 travels along contour tool path 640 in thedirection of arrow 662 between point 660 and stop point 654, overlappingthe previously deposited modeling material. As such, as extrusion head20 travels in the direction of arrow 662, the volumetric flow rate maybe decreased to reduce the amount of modeling material that isaccumulated along the vertical z-axis at seam 664. The overlappingarrangement shown in FIG. 10 further reduces porosity by effectiveoverlapping the intersection at seam 664. In additional embodiments,contour tool path 640 may further bent within interior region 650 toposition stop point 654 at or adjacent to start point 652, as discussedabove for the embodiments of layers 136 and 236 (shown in FIGS. 5 and 6,respectively).

FIGS. 11 and 12 illustrate additional alternative embodiments in whichthe contour tool path also functions as an interior raster path to fillat least a portion of the interior region. As shown in FIG. 11, layer736 includes contour tool path 740 having start point 752 locatedadjacent to exterior surface 746. As such, in this embodiment, startpoint 752 is not adjusted to a location within interior region 750.However, the stop point of contour tool path 740 (not shown) is adjustedto a location within interior region 750 and contour tool path 740 isgenerated to at least partially fill interior region 750 with a rasterpattern.

During a build operation, extrusion head 20 initially follows contourtool path 740 from start point 752 in the direction of arrow 744 to formperimeter path 738. Upon reaching point 760, extrusion head 20 thenturns and follows contour tool path 740 in the direction of arrow 762and continues to deposit the modeling material in a back-and-forthraster pattern within interior region 750. This embodiment is beneficialfor reducing the number of times that a tip of extrusion head 20 needsto be picked up and moved. Since this process can be performed with eachlayer of 3D model 26 and support structure 28, this can providesubstantial time savings when building 3D model 26 and support structure28 in system 10.

Additionally, start point 752 and the stop point for contour tool path740 may also be positioned at locations in the x-y plane that willmaximize the area of interior region 750 that is filled with the rasterpattern of contour tool path 740. For example, after generating contourtool path 740, pursuant to step 74 of method 66 (shown in FIG. 4), thestart and stop points may be repositioned around the perimeter to apoint that maximizes the raster pattern fill within interior region 750before reaching the stop point. This further reduces the number of timesthat a tip of extrusion head 20 needs to be picked up and moved forbuilding each layer. Furthermore, the generated raster pattern forcontour tool path 740 may be offset by an angle between each successivelayer (e.g., by 90 degrees). As a result, repositioning the start andstop points in this manner will cause the seams of each successive layerto be positioned at different locations in the x-y plane. This furtherconceals the seams of a 3D model (e.g., 3D model 26) by staggering thelocations of the seams between successive layers.

As shown in FIG. 12, layer 836 includes contour tool path 840 havingboth start point 852 and the stop point (not shown) located withininterior region 850, where contour tool path is generated to at leastpartially fill interior region 850 with a raster pattern, as discussedabove for layer 736 (shown in FIG. 11). In the embodiment shown in FIG.12, however, start point 852 is also located within interior region 850,desirably at an angle that substantially follows the raster pattern ofcontour tool path 840. This combines the process time savings attainablewith the integrated raster pattern along with the reduced porosity thatis achieved by positioning start point 852 within interior region 850.These benefits are in addition to the concealment of seam 864, whichallows the dimensions of perimeter path 838 at seam 864 to be truer tothe dimensions of the digital representation of 3D model 26 andincreases the consistency of the seams of successive layers of 3D model26.

As shown in FIG. 13, layer 936 includes contour tool path 940 havingstart point 952 and stop point 94 in a crimped-square arrangement. Inthis embodiment, start point 952 is positioned within interior region950 such that contour tool path 940 turns at corner points 986 a and 986b. During a build operation, extrusion head 20 initially follows contourtool path 940 from start point 952 in the direction of arrows 956 a, 956b, and 956 c, until it reaches point 958. Extrusion head 20 may formperimeter path 938 along arrows 944 until it reaches point 960.Extrusion head 20 may then turn inward until it reaches stop point 954.In an alternative embodiment, start point 952 and stop point 954 may beflipped such that the crimped square geometry is formed around startpoint 952. The arrangement depicted in FIG. 13 positions start point 952and stop point 954 within interior region 950, while also furtherreducing the porosity of layer 936 by crimped square of the depositedroads of build material within interior region 950.

FIGS. 14 and 15 illustrate layer 1036, which is an additionalalternative to layer 36 (shown in FIGS. 2 and 3), where the referencelabels are increased by 1000. As shown in FIG. 14, layer 1036 includesperimeter paths 1038 a and 1038 b, which are a pair roads of a modelingmaterial that is deposited by extrusion head 20 along contour tool path1040 in two passes, as represented by arrows 1044 (first pass to formperimeter path 1038 a) and arrows 1090 (second pass to form perimeterpath 1038 b). As further shown, perimeter path 1038 a includes exteriorsurface 1046 and perimeter path 1038 b includes interior surface 1048.Exterior surface 1046 is the outward-facing surface of perimeter path1038 a, which may be observable when 3D model 26 is completed. Interiorsurface 1048 is the inward-facing surface of perimeter path 1038 b,which defines interior region 1050. Interior region 1050 is the regionof layer 1036 confined within perimeter paths 1038 a and 1038 b, and maybe filled with additional modeling material deposited along additionallygenerated tool paths (e.g., raster paths, not shown).

As shown in FIG. 15, contour tool path 1040 includes start point 1052and stop point 1054, where stop point 1054 is located within interiorregion 1050. Accordingly, during the build operation, controller 30directs extrusion head 20 to begin depositing the modeling material atstart point 1052, and to move along contour tool path 1040 in thedirection of arrows 1044 until reaching point 1092. This substantiallyforms perimeter path 1038 a. At this point, while continuing to depositthe modeling material, extrusion head 20 steps over from perimeter path1038 a to begin forming perimeter path 1038 b at point 1094. Extrusionhead 20 then continues to moves along contour tool path 1040 in thedirection of arrows 1090 until reaching stop point 1054. This formsperimeter path 1038 b.

As shown, stop point 1054 is adjusted to a location within interiorregion 1050. As such, seam 1064 also extends inward within interiorregion 1050. This effectively eliminates the formation of bulges ofmodeling material at seam 1064. Additionally, the step-over arrangementalso reduces the porosity of 3D model 26 at seam 1064, thereby reducingor eliminating the transmission of gases and/or liquids through seam1064.

In an alternative embodiment, start point 1052 and stop point 1054 maybe flipped such that start point 1052 is located within interior region1050. In this embodiment, when extrusion head 20 reaches stop point 1054(at the location of start point 1052 in FIG. 15), extrusion head 20 maystep back again toward the location of stop point 1054 in FIG. 15,thereby creating an X-pattern at seam 1064. The volumetric flow rate ofthe modeling material is desirably reduced when stepping back again toreduce the amount of the modeling material that is accumulated along thevertical z-axis at seam 1064.

In additional alternative embodiments, the step-over arrangement may becontinued to form additional perimeter paths 1038, thereby increasingthe overall thickness of the perimeter paths. These embodiments arebeneficial for use with thin-walled regions where the formation ofraster patterns may be more time consuming. Furthermore, the embodimentsdiscussed in FIGS. 14 and 15 may be combined with the raster patternembodiments shown in FIGS. 11 and 12. In these embodiments, contour toolpath 1040 may step over into the raster pattern to fill at least aportion of interior region 1050.

FIG. 16 is an alternative sectional view of section 15 shown in FIG. 14,illustrating layer 1136, which is an alternative to layer 1036 (shown inFIGS. 14 and 15) having a different stop point, and where the referenceslabels are increased by 100. As shown in FIG. 16, contour tool path 1140of layer 1136 includes start point 1152 and stop point 1154, where startpoint 1152 is located at the same position as start point 1052 (shown inFIG. 15). Stop point 1154, however, stops the deposition of the modelingmaterial prior to forming a complete ring for perimeter path 1138 b.While shown at the particular location in FIG. 16, stop point 1054 maybe located at any distance from point 1194. This embodiment is alsosuitable for extending seam 1164 inward within interior region 1150,thereby effectively eliminating the formation of bulges of modelingmaterial at seam 1164. Additionally, the step-over arrangement alsoreduces the porosity of 3D model 26 at seam 1164 and the shortenedlength of perimeter path 1138 b is beneficial for use in thin-wallregions.

EXAMPLES

The present disclosure is more particularly described in the followingexamples that are intended as illustrations only, since numerousmodifications and variations within the scope of the present disclosurewill be apparent to those skilled in the art. Build operations werepreformed with the method of the present disclosure to fabricate 3Dmodels of Examples 1-4, each having concealed seams. Each 3D model ofExamples 1-4 were built from the same digital representation having afilled cylindrical geometry.

For each 3D model of Examples 1-4, the digital representation wasprovided to a computer capable of communicating with an extrusion-baseddigital manufacturing system. The computer then sliced the digitalrepresentation into multiple layers with a software program commerciallyavailable under the trade designation “INSIGHT” from Stratasys, Inc.,Eden Prairie, Minn. The software program also generated contour toolpaths for each sliced layer. In addition, the start and stop points ofeach contour tool path were adjusted to predefined locations within theinterior regions defined by the respective contour tool paths.

The start and stop points for Example 1 were adjusted to an open-squarearrangement as depicted in layer 36 (shown in FIG. 3). The start andstop points for Example 2 were adjusted to an overlapped closed-squarearrangement as depicted in layer 236 (shown in FIG. 6). The start andstop points for Example 3 were adjusted to an converging-pointarrangement as depicted in layer 536 (shown in FIG. 9). The start andstop points for Example 4 were adjusted to an overlapped-crossarrangement as depicted in layer 536 (shown in FIG. 10). For eachmodified contour tool path, raster tool paths were then generated withinthe interior regions, where the raster tool paths accommodated theadjustments to the start and stop locations of the contour tool paths.

In addition to the 3D models of Examples 1-4, a 3D model of ComparativeExample A was prepare from the same digital representation and using thesame above-discussed steps. However, for Comparative Example A, thestart and stop locations of the contour tool paths were not adjusted. Assuch, the start and stop locations remained collinear with the outerrings of the contour tool paths.

For each 3D model of Examples 1-4 and Comparative Example A, theresulting data was then transmitted to the extrusion-based digitalmanufacturing system, which was a fused deposition modeling systemcommercially available under the trade designation “FORTUS 400mc” fromStratasys, Inc., Eden Prairie, Minn. Based on the received data, thesystem then built each 3D model from an acrylonitrile-butadiene-styrene(ABS) copolymer modeling material.

After the build operations were completed, the perimeter path seams ofeach 3D model was visually inspected. For the 3D model of ComparativeExample A, the perimeter path seams exhibited surface bulges of modelingmaterial that were readily identifiable by the naked eye. In comparison,however, the perimeter path seams of the 3D models of each of Examples1-4 did not exhibit any surface bulging and were consistent between thesuccessive layers. As such, the method of the present disclosure issuitable for effectively concealing the seams of the perimeter paths(created by the contour tool paths). As discussed above, this mayincrease the aesthetic and functional qualities of the resulting 3Dmodels.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

The invention claimed is:
 1. A method for building a three-dimensionalmodel with an extrusion-based digital manufacturing system having anextrusion head and a controller, the method comprising: receiving a toolpath for a layer of the three-dimensional model by the controller,wherein the received tool path comprises an outgoing segment, anincoming segment, and a contour segment extending between the outgoingsegment and the incoming segment, and wherein the incoming segmentoverlaps the outgoing segment at an intersection; and moving theextrusion head in a pattern that follows the received tool path toproduce a perimeter path of a thermoplastic material for the layer,wherein the perimeter path has a concealed seam at the intersection ofthe outgoing segment and the incoming segment.
 2. The method of claim 1,wherein the perimeter path defines an interior region of the layer, andwherein portions of the perimeter path defined by the outgoing segmentof the received tool path and of the incoming segment of the receivedtool path are at least partially located within the interior region ofthe layer.
 3. The method of claim 1, wherein the overlap of the outgoingsegment of the received tool path and the incoming segment of thereceived tool path defines an X-pattern at the intersection.
 4. Themethod of claim 1, wherein the concealed seam reduces surface porosityfor the three-dimensional model.
 5. The method of claim 1, and furthercomprising reducing an amount of material that vertically accumulates atthe intersection where the incoming segment of the received tool pathoverlaps the outgoing segment of the received tool path.
 6. The methodof claim 1, and further comprising: generating the tool path with acomputer based on a predicted road width for the perimeter path; andtransmitting instructions for the generated tool path to the controller.7. The method of claim 6, wherein the predicted road width ranges fromabout 250 micrometers to about 1,020 micrometers.
 8. The method of claim1, wherein a portion of at least one of the outgoing segment of thereceived tool path and the incoming segment of the received tool pathdefines a raster pattern.
 9. A method for building a three-dimensionalmodel with an extrusion-based digital manufacturing system having anextrusion head and a controller, the method comprising: generating atool path with a computer; transmitting instructions for the generatedtool path to the controller; depositing a thermoplastic material fromthe extrusion head while moving the extrusion head along the generatedtool path to form a perimeter path of a layer of the three-dimensionalmodel, wherein the perimeter path comprises: an outgoing road portion; acontour road portion extending from the outgoing road portion; and anincoming road portion extending from the contour road portion, andoverlapping the outgoing road portion with an X-pattern, thereby forminga concealed seam for the layer.
 10. The method of claim 9, wherein theperimeter path defines an interior region of the layer, and wherein theoutgoing road portion and the incoming road portion are each at leastpartially located within the interior region of the layer.
 11. Themethod of claim 10, and further comprising depositing the thermoplasticmaterial from the extrusion head while moving the extrusion head alongat least one additional tool path to produce at least one additionalroad located within the interior region of the layer.
 12. The method ofclaim 9, wherein the incoming road portion has a reduced volume of thedeposited thermoplastic material at the overlapped X-pattern compared tothe outgoing road portion.
 13. The method of claim 9, wherein theconcealed seam for the layer reduces surface porosity of thethree-dimensional model.
 14. The method of claim 9, wherein at least oneof the outgoing road portion and the incoming road portion also definesa raster pattern.
 15. A method for building a three-dimensional modelwith an extrusion-based digital manufacturing system having an extrusionhead and a controller, the method comprising: moving an extrusion headalong an outgoing tool path segment to form an outgoing road portion fora layer of the three-dimensional model; moving the extrusion head fromthe outgoing tool path segment along a contour tool path segment to forma contour road portion for the layer; and moving the extrusion head fromthe contour tool path segment along an incoming tool path segment toform an incoming road portion for the layer that overlaps the outgoingroad portion to form a concealed seam for the layer, and such that theoutgoing road portion and the incoming road portion are each at leastpartially located within an interior region of the layer.
 16. The methodof claim 15, wherein at least one of the outgoing road portion and theincoming road portion also defines a raster pattern.
 17. The method ofclaim 15, wherein the overlap of the outgoing road portion and theincoming road portion defines an X-pattern.
 18. The method of claim 15,wherein the concealed seam reduces surface porosity for thethree-dimensional model.
 19. The method of claim 15, and furthercomprising reducing an amount of material that vertically accumulatesfor the incoming road portion at the overlap of the outgoing roadportion and the incoming road portion.
 20. The method of claim 15,wherein the outgoing road portion, the contour road portion, and theincoming road portion each comprise a thermoplastic material.